#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;


void printCombination(const vector<int>& vec, const string& bitmask) {
    vector<int> combination;
    for (int i = 0; i < vec.size(); ++i) {
        if (bitmask[i] == '1') {
            combination.push_back(vec[i]);
        }
    }
    for (int num : combination) {
        cout << num << " ";
    }
    cout << "\n";
}

int main() {
    std::vector<int> vec = {1, 2, 3, 4, 5, 6};
    int n = vec.size();
    int k = 3; 
    string bitmask;
    // The initial bitmask of k 1's followed by (n-k) 0's
    for (int i = 0; i < n; ++i) {
        if(i < k) bitmask += '1';
        else bitmask += '0';
    }
    do {
        printCombination(vec, bitmask);
    } while (std::prev_permutation(bitmask.begin(), bitmask.end()));

    return 0;
}